Method and apparatus for inspecting defects

ABSTRACT

To provide a defect inspection apparatus for inspecting defects of a specimen without lowering resolution of a lens, without depending on a polarization characteristic of a defect scattered light, and with high detection sensitivity that is realized by the following. A detection optical path is branched by at least one of spectral splitting and polarization splitting, a spatial filter in the form of a two-dimensional array is disposed after the branch, and only diffracted light is shielded by the spatial filter in the form of a two-dimensional array.

CLAIM OF PRIORITY

This application is a continuation of application Ser. No. 12/423,902,filed on Apr. 15, 2009, now allowed, which claims the benefit ofJapanese Application No. 2008-106579, filed Apr. 16, 2008, in theJapanese Patent Office, the disclosures of which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

The present invention relates to a defect inspection method and a defectinspection apparatus that uses this, and more specifically, to a defectinspection method for detecting defects of a minute pattern formed on asubstrate through a film process that is typified by a semiconductormanufacture process and a manufacture process of flat panel display,foreign materials, etc. and a defect inspection apparatus that usesthis.

As a conventional apparatus for detecting defects of a specimen, thereis a patent of International Publication WO 2003/083560. This inspectionapparatus is equipped with a dark field detecting optical system thatdetects scattered light on a wafer by illuminating the wafer surfaceslantingly with a light of a single wavelength. Diffracted light from aperiodic pattern coming into this optical system is shielded by aspatial filter disposed at a rear side focal point position (an exitpupil position). As this spatial filter, a configuration that uses aliquid crystal filter conformed to ultraviolet rays is shown.

Various patterns are formed on the semiconductor wafer and kinds ofdefects have also great varieties according to generation causes. In theoptical dark-field detection system, a laser is used as a light source,which provides an illumination light of a single wavelength.

However, with the light of the single wavelength, there is the casewhere the scattered light can hardly be obtained from the defectdepending on optical constants of a defective material and the shape andstructure around the defect. As one example, although a silicon oxidefilm is used as an electric insulation film of the patterns that arestacked, an optically transparent oxide film generates thin filminterference; therefore the intensity of the scattered light will varydepending on its film thickness. Because of this phenomenon, thescattered light becomes extremely small with a film thickness conditionof weakening light rays and becomes undetectable. As a countermeasureagainst this, the number of illumination wavelengths is increased to aplural number. By this modification, even under a film thicknesscondition under which the amount of detected light is insufficient witha single wavelength, a probability of being able to secure the amount oflight necessary for defect detection at the other wavelength(s) isincreased.

In this way, although it is possible to improve a capture ratio ofdefects with illumination of a plurality of wavelengths, the diffractedlight from the periodic pattern, such as the memory cell part, has adifferent position of a diffracted image for each wavelength because adiffraction angle is expressed by a function of wavelength. FIG. 3 showsa schematic diagram of the diffracted image when the periodic pattern isilluminated by the illumination lights of wavelengths λ₁, λ₂ (λ₁ is arelatively short wavelength) (hereinafter referred to as a λ₁ light anda λ₂ light). This diagram is a schematic diagram of the diffracted imageformed at an exit pupil 400 of an objective lens. FIG. 3A shows adiffracted image (diffracted light) 410 of the λ₁ light, and FIG. 3Bshows a diffracted image (diffracted light) 430 of the λ₂ light. Thediffracted image 410 occurs in a direction of periodicity of thepattern. An example of FIGS. 3A, 3B, and 3C is an example of thediffracted image of a pattern that is formed periodically in twodirections intersecting at right angles.

As means for shielding these diffracted images, there is a technique ofshielding the image by fitting a light shielding belt 420 to a pitch ofthe diffracted image. When lights of two wavelengths λ₁, λ₂, aresimultaneously cast for illumination, regarding the diffracted imagesactually detected, the two diffracted images of wavelength λ₁, λ₂, aredetected at the exit pupil 400 of the objective lens. Because of this,the number of the diffracted images becomes large as shown in FIG. 3C.If these images are intended to be shielded, the number of the lightshielding belts will become large and an aperture ratio of the exitpupil will lower. Since this leads to lowering of substantialresolution, there is a problem to be solved that contrast of a minutedefect decreases and defect detection sensitivity lowers.

In addition, when the liquid crystal filter is used as the spatialfilter, it is necessary that the scattered light is filtered so as tobecome a linearly polarized light and alignment of the liquid crystal iselectrically controlled to make it perform optical rotation. It becomespossible to control the transmittance of the light that is transmittedthrough a polarizing plate disposed on an image plane side depending onthe amount of this optical rotation.

However, the polarization state of the scattered light changes accordingto a shape, a structure, a material, etc. of the pattern and the defect.Therefore, if the scattered is filtered so as to become a linearlypolarized light one the object side (wafer side) of the liquid crystal,in the case where the defect scattered light is polarized in a directionperpendicular to a filter transmission axis, the scattered light of thedefect will be shielded and accordingly it will become impossible todetect the defect.

SUMMARY OF THE INVENTION

Provided is a method for detecting the defects of a specimen with acircuit pattern formed on it, where lights of a plurality of wavelengthsare illuminated onto the specimen slantingly, scattered and diffractedlight from the pattern and the defect are captured by an objective lens,the diffracted light for a periodic pattern is shielded by a spatialfiltering device in the form of an array, light that was not shielded issubjected to branching by at least one or more of spectral splitting andpolarization splitting, and images are detected on image planes of therespective optical paths that were branched in the above and areprocessed to determine a defect candidate.

Moreover, the spatial filtering device is a group of optical shutterseach using a liquid crystal or double refection element or of opticalshutters each using MEMS, and has a structure in which the opticalshutters are arranged in the form of a two-dimensional array and thatcan electrically control transmitted light of the device.

It is characterized by using a reflection type DMD as the spatialfiltering device and utilizing polarization for branching the incidentlight to the DMD and the reflected light after the filtering.

Moreover, it is characterized by that the spatial filtering device is aliquid crystal tunable filter in which Lyot filters are arrangedone-dimensionally or two-dimensionally.

Moreover, it is characterized by that a light source for illuminating aspecimen is a lamp, or a plurality of lasers, or a laser that emitslaser beams of a plurality of wavelengths.

Moreover, it ids characterized by that defect determination is performedusing plural kinds of images that differ from one another in at leastone condition of the wavelength condition and the polarizationcondition; when the defect candidate is determined by comparisonprocessing of the plural kinds, a determination result and the imagethat was subjected to determination processing are stored; and regardingthe image that was not determined as a defect, then image in theidentical space as in the defect candidate is stored, a feature quantityof the image in the identical space but under a different condition iscomputed, and the defect determination or sorting is performed again.

According to the present invention, it is possible to improve a captureratio of defects by stably detecting scattered light to be detected thatvaries according to a shape, a structure, and a material of the defectwith an illumination of a plurality of wavelengths.

Moreover, also in the case of the illumination with lights of aplurality of wavelengths, inspection sensitivity is improved byshielding the diffracted light of a normal pattern while suppressinglowering of an aperture ratio of a detection optical system and therebydetecting the scattered light of minute defects efficiently.

Further, in the case where the polarization state of scattered lightdiffers from others depending on a defect kind, it is possible toimprove the capture ratio of defects by performing spatial filteringwithout shielding the scattered light of the defect.

These and other objects, features and advantages of the invention willbe apparent from the following more particular description of preferredembodiments of the invention, as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an outline configuration of an opticalsystem shown in this first embodiment;

FIG. 2 is a diagram showing an outline configuration of an inspectionapparatus shown in this first embodiment;

FIG. 3A is a schematic diagram of a diffracted image formed at an exitpupil of an objective lens when a periodic pattern is illuminated by anillumination light of a wavelength λ₁;

FIG. 3B is a schematic diagram of a diffracted image formed at the exitpupil of the objective lens when the periodic pattern is illuminated byan illumination light of a wavelength λ₂ and an explanatory diagram ofthe diffracted image and spatial filtering at the exit pupil position;

FIG. 3C is the diffracted image that is detected at the exit pupil ofthe objective lens when the periodic pattern is illuminatedsimultaneously by the illumination light of a wavelength λ₁ and theillumination light of a wavelength λ₂;

FIG. 3D is a diagram showing one example of a spatial filter whosefiltering pattern can be changed to a suitable one during inspectionaccording to the pitch and shape of a pattern on a wafer;

FIG. 4A shows an example in which a liquid crystal filter 500 a is usedas a spatial filtering device;

FIG. 4B shows a structure of the two-dimensional spatial filterutilizing an electro-optic effect;

FIG. 4C shows a structure of a two-dimensional spatial filter 500 cusing a MEMS;

FIG. 4D is a diagram showing a configuration of one pixel of the MEMS inwhich pixels are arranged in the form of a two dimensional array;

FIG. 5 is a diagram showing an outline configuration of atwo-dimensional array liquid crystal tunable filter;

FIG. 6A shows a spectral transmission characteristic under a conditionthat allows a λ₁ light to be transmitted;

FIG. 6B shows a spectral transmission characteristic under a conditionthat allows a λ₂ light to be transmitted;

FIG. 6C shows a spectral transmission characteristic under a conditionthat allows both the λ₁ light and the λ₂ light to be transmitted;

FIG. 6D shows a case where the two-dimensional array liquid crystaltunable filter is used as the spatial filter;

FIG. 7 is a diagram showing the outline of an optical system shown inthis fourth embodiment;

FIG. 8A shows an azimuth of the illumination light relative to the waferand a definition of polarization of the illumination light;

FIG. 8B defines a direction of a transmission axis of an analyzer;

FIG. 8C shows an amount of analyzer transmitted light of patternscattered light when Y-direction illumination is performed byS-polarization illumination and P-polarization illumination;

FIG. 8D shows the amount of the analyzer transmitted light of thepattern scattered light when the S-polarization and P-polarizationilluminations are performed using the 45-degree azimuth illumination;

FIG. 9A shows a plan view when the Y-direction illumination with the λ₁light and the 45-degree azimuth illumination with the λ₂ light areperformed simultaneously at spatially separated positions on the wafer;

FIG. 9B shows a plan view when the Y-direction illumination with the λ₁light and the 45-degree azimuth illumination with the λ₂ light areperformed at spatially separated positions on the wafer by theS-polarization relative to the wafer;

FIG. 10 is a diagram showing an outline configuration of an opticalsystem that will be shown in this fifth embodiment;

FIG. 11 is a diagram showing an outline configuration of an opticalsystem using a reflection type two-dimensional array spatial filter;

FIG. 12 is a diagram showing an outline configuration of an opticalsystem that will be shown in this seventh embodiment;

FIG. 13 is a diagram showing an optical characteristic of a spectraltransmission filter;

FIG. 14 is a diagram showing disposition of a spectral transmissionfilter unit;

FIG. 15 is a diagram showing an outline configuration of the spectraltransmission filter unit;

FIG. 16 is a diagram showing an outline configuration of an optical pathdifference compensation unit;

FIG. 17A shows a layout of the wafer and a die;

FIG. 17B is a diagram showing a state in which memory mat parts in thedie are formed in the form of a matrix and peripheral circuits areformed between them;

FIG. 17C is a diagram showing a state where an illumination width in astage scan direction is narrowed; and

FIG. 18 is a flowchart showing a procedure of optimization of condition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, embodiments will be described in detail using drawings.

First Embodiment

FIG. 1 shows a configuration of an apparatus for detecting defects of aspecimen according to the present invention. A pattern 2 is formed on awafer 1 and a defect 3 exists on the pattern 2. The wafer 1 isilluminated by an illumination optical system 5 of a plurality ofwavelengths (in this embodiment, two wavelengths λ₁, λ₂) that isdisposed slantingly relative to the wafer 1. For a light source 7 usedin an illumination optical system 5, lights ranging from DUV (DeepUltraviolet) lights to the visible lights such as: mercury lampsemitting the d line (588 nm), the e line (546 nm), the g line (436 nm),the h line (405 nm), and the i line (365 nm); a second harmonic 532 nmlaser of YAG; a third harmonic (355 nm) or fourth harmonic (266 nm)laser; and a 199 nm laser. Among them, lights of two wavelengths (λ₁,λ₂) are cast on the wafer 1 for illumination from the illuminationoptical system. Among pieces of light scattered by the pattern 2 and thedefect 3, light that propagates to an objective lens 10 within its NA(Numerical Aperture) is captured by the objective lens 10 and forms adiffracted image at a rear side focal (an exit pupil) position of theobjective lens 10. A spatial filter 20 is disposed at this rear sidefocal point position or its conjugate position, and diffracted lightfrom the periodic normal pattern 2 is shield. The light that istransmitted through the spatial filter 20 is branched to optical pathsby a dichroic mirror 25 depending on its wavelength. The light of awavelength λ₁ (hereinafter referred to as the λ₁ light) that wastransmitted through the dichroic mirror 25 forms an image of the wafer 1on an image sensor 100 through an image formation lens 30. On the otherhand, the light of a wavelength λ₂ (hereinafter referred to as the λ₂light) that reflected dichroic mirror 25 forms a scattered image on animage sensor 110 though an image formation lens 35.

FIG. 2 shows a configuration of an inspection apparatus using thisoptical system. The wafer 1 is mounted on a stage 4 of the inspectionapparatus, which performs θ alignment between the pattern 2 formed onthe wafer 1 and the stage scan direction. A dark field image of thewafer 1 enables an image of the scattered light to be detectedcontinuously while the stage 4 is being scanned at a constant speed inthe X-direction. As a light source, a laser 8 that emits a laser beam ofa specific wavelength λ₁ (e.g., the third harmonic 355 nm of YAG) in awavelength band from DUV (Deep Ultraviolet) to UV lights is used, and anoutputted laser beam of a wavelength λ₁ (λ₁ laser beam) reflects on amirror 201 and on a dichroic mirror 205. Moreover, a λ₂ laser beamoutputted from a laser of a wavelength λ₂ that emits the λ₂ laser beam(e.g., the second harmonic 532 nm of YAG) different from that of thelaser 8 of a wavelength of λ₁ is transmitted through the dichroic mirror205, and propagates on the same optical axis as that of the λ₁ laserbeam. The laser beams of two wavelengths λ₁, λ₂ reflect on a mirror 207,are transmitted through a ½ wave plate 210, and are branched to twooptical paths by a half mirror 220 with small wavelength dependency. Theλ₁, λ₂ lights that reflected on the half mirror 220 reflect on a mirror270 equipped with a mirror position control mechanism 260, and aretransmitted through a ½ wave plate 280 and a ¼ wave plate 290. Thesewave plates 280, 290 converts the lights to a predetermined S/Pcircularly polarized lights to the wafer 1 or lights in intermediatepolarization states between them. The lights come incident on a lens 295and illuminate the wafer 1 in the shape of a strip with its longitudinalside lying in the Y-direction.

On the other hand, the λ₁, λ₂ laser beams that were transmitted throughthe half mirror 220 are transmitted through a ¼ wave plate 225, reflectson a mirror 230, reflect on a mirror 250 equipped with a mirror positioncontrol mechanism 240, and illuminate the wafer 1 through a lens 255 inthe shape of a strip with its longitudinal side lying in theY-direction. The mirror position control mechanisms 240, 260 can controlmirrors that are attached to each of them in height and angle, and makeit possible to control elevation angles from which the wafer 1 isilluminated, respectively. Although, in this embodiment, simultaneousillumination from two directions of X and Y using the half mirror 220was described as the embodiment, an embodiment in which onlyillumination from the X-direction is done by removing the half mirror220 out of the optical path and also an embodiment in which illuminationfrom the Y-direction is done by disposing a mirror that reflects allinstead of the half mirror 220 are conceivable.

Further, in this embodiment, although the illuminations whose azimuthslie in the X- and Y-directions, respectively, is shown, a form in whichillumination is made from an azimuth shifted from the Y-axis, forexample, by 45 degrees or 20 degrees is conceivable as a modification ofthis embodiment. In addition, it becomes possible by using a dichroicmirror instead of the half mirror 220 to perform an illumination whosewavelength is different for each illumination azimuth. A reason ofchanging the illumination elevation angle and the illumination azimuthis to provide a function of setting a condition advantageous toinspection according to the defect and pattern that becomes aninspection object because a scattering distribution is differentaccording to directionality of the defect and pattern, a shape of thedefect, and unevenness (e.g., a foreign material taking a shape of aconvexity in the Z-direction and a scratch taking a shape of concavity).The scattered light from the defect 3 or the pattern 2 forms a scatteredimage on the image sensor 100 with the light of a wavelength λ₁ that istransmitted through a dichroic mirror 32 after through the objectivelens 10, the spatial filter 20, and the dichroic mirror 32. A scatteredimage by the light of a wavelength λ₂ that reflected on the dichroicmirror 25 is formed on the image sensor 110. The detected image isinputted into an image processing section 300, which compares it with animage of an identical design pattern, for example, an image of anadjacent die, and detects the defect 3. Defect information, such ascoordinates, dimensions, and brightness of the detected defect, is sentto a control section 320. Then the inspection apparatus user is enabledto make the apparatus display the defect information, such as a defectmap on the wafer, and to make it output defect information data.

Moreover, the control section 320 is also equipped with a function ofperforming operation instruction of the inspection apparatus, and givesinstructions of operations to a mechanism control section 330, whichcontrols operations of the stage 4 and an optical system mechanismcontrol section 340. As a spatial filter that this optical system uses,there are a micro shutter array that utilizes an electro-optic effect ofthe double refraction element (LiNbO₃, PLZT, etc.) and filters in theform of a one-dimensional array and in the form of a two-dimensionalarray each of which uses a liquid crystal filter and an MEMS (MicroElectro Mechanical Systems), as embodiments. In these devices, sincetransmission/shielding of the light can be switched by electricalcontrol at high speed, it becomes possible to changeover the filteringpattern to a suitable one according to the pitch and shape of thepattern 2 on the wafer 1 during the inspection. FIG. 3D shows its form.A two-dimensional spatial filter 500 is disposed on the rear side focalplane (an exit pupil plane) or at its conjugate position of theobjective lens 10 where the diffracted image is formed. A setting ofshielding a pixel 510 of the two-dimensional spatial filter 500 at aposition at which the diffracted image is formed is made. By thissetting, an aperture ratio of the exit pupil becomes larger thanshielding of diffracted images 410, 430 made by a light shielding belt420 shown in FIG. 3C, and therefore lowering of the resolution of theoptical system can be suppressed.

Second Embodiment

FIG. 4A shows an example in which a liquid crystal filter 500 a is usedas a spatial filtering device. Only the linearly polarized lightcorresponding to a transmission axis of a liquid crystal filter incidentlight 150 is transmitted through a first polarizing plate 155. In a TFT(Thin Film Transistor) substrate 160, an impressed voltage of anillumination electrode 180 is controlled to change alignment of a liquidcrystal 170 that is sealed in between two orienting films 165, 175. Thisconfiguration makes it possible to control the transmittance of thefilter transmitted light that is transmitted through a second polarizingplate 185 according to the alignment of this liquid crystal 170. Thisliquid crystal filter 500 a is such that pixels are arranged in the formof a two-dimensional array, and the transmittance of the light can becontrolled for every pixel 505.

FIG. 4B shows a structure of a two-dimensional spatial filter 500 b thatutilizes the electro-optic effect. Regarding the incident light 150, itslinear polarization component is transmitted through the firstpolarizing plate 155, and comes incident on a double refraction material172 that has the electro-optic effect, such as PLZT (abbreviation of(Pb, La) (Zr, Ti)O₃) and LiNbO₃. This double refraction material 172 issuch that pixels are arranged in the form of a one-dimensional ortwo-dimensional array, which makes it possible to control an oscillatingdirection of the linearly polarized light having entered according tothe impression voltage of the electrode formed for each pixel, andaccordingly to change the transmittance of the second polarizing plate185.

FIG. 4C shows a structure of a two-dimensional spatial filter 500 cusing the MEMS. The MEMS has pixels that are arranged in the form of atwo-dimensional array, and in every pixel 506, a shielding part 507shown in FIG. 4D and an electrode 508 are formed. Impression of apredetermined voltage to the shielding part 507 and the electrode 508causes the shielding part 507 to fall on the electrode 508 side by theaction of electrostatic capacity, which makes it possible to transmitthe incident light. For this reason, it becomes possible, by controllingthe impressed voltage to the shielded part 507 and the electrode 508,for open/close states of the shielded part 507 to be switched and fortransmission/shielding of the incident light to be controlled on a pixelbasis.

Third Embodiment

With the two-dimensional spatial filter shown in FIG. 3D and FIG. 4, thepixel 510 to be shielded is shielded for the lights of two wavelengthsλ₁, λ₂. However, since positions of the diffracted lights of wavelengthsλ₁, λ₂ do not coincide with each other, the pixel on which thediffracted image of a wavelength λ₁ is formed shields only the λ₁ light,and the pixel on which the diffracted image of a wavelength λ₂ is formedshields only the λ₂ light; therefore, a substantial aperture becomeslarger.

FIG. 5 shows an example in which a two-dimensional array liquid crystaltunable filter 500 d that is formed by arranging liquid crystal tunablefilters LCTF's (Liquid Crystal Tunable Filter) using a principle of theLyot filter in the form of a two-dimensional array is used as thespatial filter. When the lights of wavelengths λ₁, λ₂ come incident on afirst polarizing plate 550, the two lights become the linearly polarizedlights, enter the wave plate 555, and are given a phase differencebetween them. In a TFT (Thin Film Transistor) substrate 560, by makingalignment of a liquid crystal 575 sealed in between an orienting film570 and an orienting film 580 be switched, lights that are transmittedthough a transparent electrode 585 and a second polarizing plate 590 aredetected. This configuration enables transmission/shielding to becontrolled by selecting a wavelength.

FIG. 6A shows a spectral transmission characteristic using a conditionthat allows the λ₁ light to be transmitted. FIG. 6B is a spectraltransmittance under a condition that allows the λ₂ light to betransmitted, and FIG. 6C is the same characteristic under a conditionthat allows both the λ₁, λ₂ lights to be transmitted. FIG. 6D shows astate when the two-dimensional array liquid crystal tunable filter 500 dis used as the spatial filter. By adopting an optical condition in whicheach light is shielded at a pixel corresponding to a position at whichthe diffracted images 410, 430 of the λ₁, λ₂ lights are formed, itbecomes possible to shield the λ₁ light and to allow the λ₂ light to betransmitted, for example, and accordingly it becomes possible tosuppress unnecessary shielding of the aperture.

Fourth Embodiment

Since the spatial filter shown in FIGS. 4A, 4B and FIG. 5 needs theincident light to become a linearly polarized light, a polarizing plateis disposed on the incidence side thereof. The scattered light from thedefect that will be an object of detection has a polarizationcharacteristic and its polarization state changes depending on the kindof the defect. For example, there occur phenomena that when the defectis illuminated with the linearly polarized light, the scattered lightmay become an elliptically polarized light and that the major axis of anellipse may rotate (optical rotation).

For this reason, when only specific polarization is detected, there willbe a possibility of overlooking defects because the defect scatteredlight is shielded. Because of this, there is an optical system forpreventing the overlooking even when the spatial filter 500 shown inFIGS. 4A, 4B and FIG. 5 is used. FIG. 7 shows a configuration of it. Apolarizing beam splitter 15 is disposed in the detection optical path,aiming to split the light into two pieces of linearly polarized light.The detection system is divided for the two optical paths and thespatial filters 500 are disposed in the respective optical paths. Thisrealizes a configuration capable of detecting the scattered light fromvarious defects without shielding it. Dichroic mirrors 25 a, 25 b aredisposed in the respective optical paths to perform spectral splittingand image sensors 100 a, 110 a, 100 b, and 110 b are disposed in therespective optical paths to detect scattered images.

Incidentally, a ¼ wave plate 11 attached with a rotation function 12 anda ½ wave plate attached with a rotation function 13 are disposed betweenthe objective lens 10 and the polarizing beam splitter 15. Thisoperation will be explained using FIG. 8. FIG. 8A shows definitions ofan orientation of illumination light and polarization of theillumination light to the wafer 1. An illumination light 130 ailluminates the wafer 1 from the Y-direction slantingly. An insert 140 ashows a cross section of this illumination light, being perpendicular toits optical axis. Taking the S-polarization relative to the wafer 1 as areference, if the polarization (the oscillating direction of an electricfield vector) rotates clockwise by 90 degrees, it will becomeP-polarization illumination. The oscillating direction of polarizationin the case of S-polarization illumination becomes as shown by an insert135 a. On the other hand, when an illumination azimuth rotates by θ₁,the oscillating direction of the S-polarization of an illumination light130 b becomes as shown by an insert 135 b. FIG. 8B defines a directionof the transmission axis of an analyzer (a polarizing plate disposed ina detection optical path on which the objective lens 10 captures thescattered light). This diagram is a plan view seen from the image sensor100 a side assuming that the analyzer is set on a transmission side ofthe polarizing beam splitter shown in FIG. 7. The X-direction beingconsidered as a reference of the analyzer transmission axis, an angle bywhich the analyzer (in the example of FIG. 7, the polarizing beamsplitter 15) is rotated clockwise is designated by θ₂. FIG. 8C shows anamount of analyzer transmitted light of pattern scattered light in thecase where the pattern is illuminated by the S-polarization and theP-polarization in the Y-direction illumination. Regarding the scatteredlight from the pattern 2 that is parallel or perpendicular to the X- andY-directions, its transmitted light becomes maximum in theS-polarization illumination with an analyzer rotation angle θ₂ set 0degree, and becomes minimum in the P-polarization illumination with thesame analyzer rotation angle. Moreover, the amount of the transmittedlight becomes minimum in the S-polarization illumination with theanalyzer rotation angle θ₂ set to 90 degrees, and becomes maximum in theP-polarization illumination.

On the other hand, in the case where the illumination light 130 b comingfrom the θ₁ azimuth (in this example, 45 degrees) shown in FIG. 8A isthe S-polarization, the amount of the transmitted light becomes maximumwhen the analyzer rotation angle θ₂ is equal to θ₁ (in this example, 45degrees). By the P-polarization illumination, the amount of thetransmitted light becomes minimum with the same analyzer rotation angle.For this reason, even when the same S-polarization illumination to thewafer 1 is used, if the illumination azimuth is different, an angle atwhich the amount of the transmitted light of the analyzer becomesmaximum or minimum will be different. Brightness variation of thetransmitted light of the pattern caused by LER (Line Edge Roughness) ofthe pattern, a minute difference of a shape thereof, grain on thesurface, and film thickness variation of an interlayer insulating filmthat do not effect criticality for the semiconductor device becomes asensitivity hindrance factor (noise light) in detecting the defects.These noise lights have the same characteristics as those of FIGS. 8Cand 8D. For this reason, when the S-polarization illumination isperformed from the Y-direction relative to the wafer 1 in theconfiguration of FIG. 7, it is possible for the S-polarization reflectedon the polarizing beam splitter 15 to minimize the scattered light andthe noise lights from the pattern parallel to or perpendicular to the X-and Y-directions (disposition of the analyzer to establish a cross Nicolstate). On the other hand, defects have various directions, andregarding polarization of the defect scattered light, S-polarizationthat reflects on the polarizing beam splitter 15 does not necessarilycause the minimum. For this reason, the reflected light (S-polarization)of the polarizing beam splitter 15 has a small amount of reflected lightof noise light, and an amount of reflected light of the defect scatteredlight increases. Therefore, a scattered image by S-polarization thatreflected on the polarizing beam splitter 15 becomes a high S/N imagethat is advantageous to defect detection. Incidentally, it may occurthat the P-polarization being transmitted through the polarizing beamsplitter 15 (deposition of the analyzer so as to be in a parallel Nicolstate) yields high S/N depending a shape, a kind, and a material of thedefect. For this reason, by detecting simultaneously each of images thatare analyzed in conditions of the cross Nicol state (reflection) and ofthe parallel Nicol state and determining the defects, it becomespossible to improve a capture ratio of the defects existing on the wafer1.

However, when the Y-direction changes to a direction away from theY-direction by 45 degrees in FIG. 7 and FIG. 8A, the analyzingdirections of the cross Nicol state and the parallel Nicol state change,respectively, even with the same S-polarization illumination relative tothe wafer 1. For this reason, by disposing a ½ wave plate 14 attachedwith the rotation function 13 between the objective lens 10 and thepolarizing beam splitter 15 and controlling a rotation angle, even whenthe illumination azimuth changes, the ½ wave plate 14 is rotated so thatthe parallel/cross Nicol state is established without rotating thepolarizing beam splitter.

Moreover, in the 45-degree azimuth illumination, as shown in FIG. 8D, aratio (a₂/b₂; ellipticity) of a maximum amount of the transmitted lightb₂ and a minimum amount of transmitted light a₂ of the analyzed lightbecomes larger than a ratio of b₁ and a₁ shown in FIG. 8C. Therefore,polarization of the pattern scattered light has a comparatively largeellipticity. In such a case, since noise light cannot be suppressedsufficiently in the cross Nicol state, the rotary mechanism 12 is usedto control rotation of the ¼ wave plate 11 so that it may converts theelliptically polarized light into a linearly polarized light. Thisenables the high S/N image to be detected with noise light suppressed,which results in improvement of defect detection sensitivity.

Fifth Embodiment

FIG. 9A shows a plan view of an illumination in the case where aY-direction illumination 130 a with the λ₁ light and the 45-degreeazimuth illumination 130 b with the λ₂ light are performedsimultaneously at spatially separated positions on the wafer 1. It isconfigured so that the Y-direction illumination 130 a may be theS-polarization illumination relative to the wafer 1, and for the45-degree azimuth illumination 130 b, its projection vector to the wafer1 may become parallel to the S-polarization of the Y-directionillumination 130. For this reason, the polarization of the 45-degreeazimuth illumination becomes intermediate polarization between the S-and P-polarizations relative to the wafer 1. In this case, since thescattered lights of two-direction illumination lights 130 a, 130 b agreewith each other in the oscillating direction of the polarization thatestablishes the cross Nicol state, it is possible to detect scatteredimages in the cross Nicol state and in the parallel Nicol state for boththe Y-direction and 45-degree azimuth illuminations in the configurationusing the polarizing beam splitter 15 shown in FIG. 7.

On the other hand, as shown in FIG. 9B, it may occur that the defectdetection sensitivity can be improved by both the Y-directionillumination 130 a of the λ₁ light and the 45-degree azimuthillumination 130 b of the λ₂ light illuminating the wafer 1 by theS-polarization relative to the wafer 1. Under a simultaneousillumination condition using these two azimuths, such a detection thateach illumination azimuth establishes the cross Nicol state cannot beperformed with the configuration shown in FIG. 7. For this reason, aconfiguration of the optical system such that each illumination azimuthestablishes the cross Nicol state is used. FIG. 10 shows this opticalsystem. The dichroic mirror 25 allows the λ₁ light to be transmittedthrough it and reflects the λ₂ light. A spatial filter 500 a is disposedin the optical path of the λ₁ light that is transmitted, and is equippedwith a ¼ wave plate 720 a, a ½ wave plate 725 a, and a rotary mechanism750 a that rotates them independently and fixes these positions. Usingthese rotatable ¼ wave plate 720 a and ½ wave plate 725 a, a conditionwhereby the detected scattered light becomes in the cross/parallel Nicolstate relative to a polarizing beam splitter 730 a or an intermediateanalyzing condition that realizes higher S/N is set up. The imagesensors 100 a, 110 a are disposed on respective image planes of thelights that were branched by the polarizing beam splitter 730 a bypolarization splitting, and two kinds of analyzed dark field images thatare formed by the λ₁ light are detected. Similarly, for the λ₂ lightthat reflected on the dichroic mirror 25, a spatial filter 500 b, a ¼wave plate 720 b, a ½ wave plate 725 b, a rotary mechanism 750 b, and apolarizing beam splitter 730 b are disposed, and image sensors 100 b,110 b are disposed on the respective image planes. With the abovetechniques, it becomes possible to detect four kinds of images thatdiffer in illumination azimuth, wavelength, and polarization.

Sixth Embodiment

FIG. 11 shows a configuration of the optical system that uses areflection type spatial light modulator utilizing a DMD (DigitalMicromirror Device) in the form of a two-dimensional array as thespatial filter. The scattered light captured by the objective lens 10 istransmitted through the ¼ wave plate 11 attached with the rotarymechanism 12 and the ½ wave plate attached with the rotary mechanism 13and comes incident on the polarizing beam splitter 15. A P-polarizationcomponent that was transmitted through the polarizing beam splitter 15becomes a circularly polarized light by a ¼ wave plate 18 a, and comesincident on a reflection type spatial light modulator 532 a that isdisposed at the rear side focal point position or its conjugate positionof the objective lens 10. The reflection type spatial light modulator532 a is such that an individual mirror plane slants by electriccontrol, and when the diffracted light from a wafer-like pattern isintended to be shielded, the mirror becomes slant to diverge thediffracted light out of the optical path. The mirror plane is set sothat light that is intended to be detected may come incident on themirror perpendicularly with the mirror being not slanted, and thereflected light propagates on the same optical path as the optical pathon which the incident light propagated in the reverse direction. Thelight that is transmitted through the ¼ wave plate 18 a again becomesS-polarization relative to the polarizing beam splitter 15, and reflectson it. The reflected light comes incident on an image formation lens 30a and the dichroic mirror 25 a. On the image planes of the λ₁ lighthaving been transmitted through the dichroic mirror 25 a and the λ₂light having reflected thereon, the image sensors 100 a, 110 a aredisposed, respectively, and the dark field images are detected.

On the other hand, the S-polarization that comes incident on thepolarizing beam splitter 15 from the objective lens 10 side and reflectsthere becomes the P-polarization relative to a second polarizing beamsplitter 16 with a ½ wave plate 17, and is transmitted through thepolarizing beam splitter 16. This light becomes the circularly polarizedlight with a ¼ wave plate 18 b, and a reflection type spatial lightmodulator 532 b reflects only the diffracted light that is not intendedto be detected out of the optical path to effect the shielding. Thelight becomes the S-polarization again with the ¼ wave plate 18 b, andreflects on the polarizing beam splitter 16. Further, on the imageplanes of the λ₁ light having been transmitted through the dichroicmirror 25 b and of the λ₂ light having reflected thereon, the imagesensors 100 b, 110 b are disposed, respectively, and the dark fieldimages are detected.

Seventh Embodiment

FIG. 12 shows a block diagram that illustrates a procedure of processingimages detected by these image sensors and determining the defect. Theimage detected by the image sensor 100 a is subjected to conversion ofbrightness, e.g., γ correction, at a gray-scale conversion section 301a. One portion of the image after the conversion is sent to an alignmentsection 305 a, and other portion is sent to a memory section 303 a. Inthe alignment section 305 a, the converted image is stored in the memorysection 303 a until the converted image has the same pattern as that ofthe already sent image (e.g., the adjacent die) in terms of design, andis put into alignment with the image sent from the memory section 303 a.A comparison section 307 a performs comparison processing on adifference image etc. of the two images that were aligned to each other,and computes a feature quantity of the image as a result of thecomparison. A defect determination section 315 determines a defect usingthis feature quantity (e.g., a maximum, an area, etc. of a gray-scaledifference). This series of processings are similarly performed for eachof the image sensors 100 b, 110 a, and 110 b.

Further, a result obtained by performing comparison for each image issent to an alignment section 310, which aligns four images different inpolarization and wavelength, compares the feature quantities of theimages obtained under these different optical conditions, and sendstheses feature quantities to the defect determination section 315. Thedefect determination section 315 determines the defects. As describedabove, the defect determination section performs the determination usingthe five kinds of feature quantities. If the image is determined to bethe defect by any of the determination results, its feature quantitiesis sent to a sorting section 317 together with remaining four kinds offeature quantities. This sorting section 317 sorts the kinds of defects(e.g., a foreign material, etching residue, a scratch, etc.) and pseudodefects (brightness unevenness of an oxide film, roughness of thepattern, grain, etc. that have no criticality for a device), and outputscoordinates of defects, a sorting result, feature quantities, etc.

Eighth Embodiment

Next, a technique of spatial filtering that uses wavelength selectivefilters, such as interference filters and sharp-cut filters, will beexplained. FIG. 13 shows two kinds of spectral characteristics. Thespectral characteristic of a λ₁ transmission filter has a characteristicof cutting the λ₂ light and the spectral characteristic of a λ₂transmission filter has a characteristic of cutting the λ₁ light. FIG.14 has an example of deposition of the filters having these spectraltransmission characteristics. Both the λ₁ transmission filter 615 andthe λ₂ transmission filter 620 are disposed at the rear side focal pointposition of the objective lens being adjacent to each other. The bothtransmission filters are positioned so that the λ₁ transmission filter615 may shield the λ₂ diffracted image 430 and the λ₂ transmissionfilter 620 may shield the λ₁ diffracted image 410.

FIG. 15 shows a schematic diagram of a positional relation of thisdiffracted light and the transmission filters when seeing the exit pupilof the objective lens projected to a plane. The λ₁, λ₂ transmissionfilters 615, 620 are of a shape of a strip and the plurality of filtersare disposed correspondingly to the diffracted lights. Thesetransmission filters 615, 620 have configurations such that positions ofthe transmission filters are adjustable, respectively, in the case ofthe λ₁ transmission filter 615, correspondingly to a pitch of the λ₂diffracted image 430 and in the case of the λ₂ transmission filter 620,correspondingly to a pitch of the λ₁ diffracted image. However, theoptical paths of the light being transmitted through the λ₁ transmissionfilter 615 and the light being transmitted through something other thanthe transmission filter bring about an optical path difference thatdepends on a refractive index difference of the filter 615 and air andthe thickness of the filter. Therefore, the image formed on the imageplane deteriorates.

FIG. 16 shows this countermeasure. In a spectral transmission filterunit 630, the λ₁ transmission filter 615 and the λ₂ transmission filter620 are disposed. An optical path difference correction liquid 631 ofthe almost same refractive index as the refractive indices of thesefilters is filled up in the spectral transmission filter unit 630, andreduces the optical path difference of the filter transmitted light andlights other than it.

Ninth Embodiment

FIG. 17A shows the wafer 1 and a layout of a die 770. As shown in FIG.7B, memory mat parts 780 are formed in a matrix manner in the die 770,and a peripheral circuit part 790 is formed between them. A waferscanning direction 800 at the time of the inspection is assumed aright-hand side, and a field of view at this time is designated as 810.At this time, paying attention to part A of the memory mat edge, sincethe spatial filtering is performed at the rear side focal pointposition, diffracted images of the memory mat part 780 and theperipheral circuit part 790 in the field of view are detected as beingoverlapped. In this case, when the spatial filter is set so that thediffracted light of the memory mat part 780 may be shielded, thediffracted light from the peripheral circuit part 810 whose patternpitch is different from that the memory mat part 780 will not beshielded, and defect detection performance of the peripheral circuitpart 810 will lower. As a countermeasure against this, there is a formin which an illumination width L in the stage scan direction shown inFIG. 17C is made narrower. Expressing the stage scan speed by V mm/s anda switching response frequency of a light shielding part of the spatialfilter by R Hz, the illumination width L in the stage scanning directionis set to V/R or less. For example, when V: 1000 mm/s and R: 100 kHz(e.g., the electro-optic effect of LiNbO₃) are set, the illuminationwidth L becomes 10 mm. If the illumination width is narrowed smallerthan this width 10 mm, the filtering that corresponds to each of thememory mat part 780 and the peripheral circuit part 790 at a boundarypart of the both can not be done because of a switching speed of thespatial filter.

Moreover, even if the illumination is performed with the illuminationwidth L narrowed further, there will be no problem in terms of thespatial filtering. However, since the intensity of illumination on thewafer 1 will become higher, it will pose a problem of damages on thewafer 1. For this reason, illumination widths ranging from 10 mm to aminimum line width that provides an illumination intensity giving nodamage are suitable illumination widths L. By this, it becomes possibleto lower a ratio by which the memory mat part 780 and the peripheralcircuit part 790 overlap each other in a width direction in the field ofview of detection and to detect the scattered image to which two kindsof the diffracted light are shielded, respectively, by switching aspatial filter condition by which the diffracted light of the memory matpart is shielded even at an edge of the memory mat part a spatial filtercondition by which the diffracted light from the peripheral circuit partis shielded even at an edge of the peripheral circuit part. The aboveenables the wafer to be inspected with high sensitivity even on theboundary between the memory mat part 780 and the peripheral circuit part790.

Tenth Embodiment

FIG. 18 shows a technique of optimization of condition by which acondition of the spatial filter is determined. The apparatus places thepattern that is intended to shield the diffracted image in the field ofview, takes in a pupil image, detects a position of the diffracted lightfrom the taken-in image, and determines the light shielding part. Acondition whereby a pixel of the spatial filter corresponding to theposition at which the determination is made is shielded is set up. Thepupil image is captured again, and a quality determination of the setupstate as to whether there is no leak of the diffracted light isperformed. If it is determined not good, the flow returns to the settingof the liquid crystal filter. If it is determined good, anotherinspection condition is set up, a test inspection and sensitivityadjustment are performed, and the optimization of condition is ended.

Incidentally, in the case where a plurality of pattern pitches exist inthe same wafer and shielding conditions of the spatial filter areintended to be set up for respective pitches, the spatial filter is setup for the each pattern pitch. In this case, the setup conditions of thespatial filter is switched in an instance, i.e., within responsibilityof 10 ms or less, based on coordinates of the wafer 1 in an actualinspection. Moreover, although being omitted in FIG. 14, the setup ofthe spatial filter needs to be performed for every wavelength. Althoughvarious combinations are conceivable about the configurations, thefunctions, and the contents of image processing that were shown in theabove embodiments, it is evident that those combinations are within thescope of the present invention.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description and all changeswhich come within the meaning and range of equivalency of the claims aretherefore intended to be embraced therein.

1. A method that detects defects of a specimen, comprising the steps:illuminating the specimen surface with a plurality of illuminationlights each having a different wavelength; detecting a plurality ofimages by detecting a plurality of scattered lights each having adifferent wavelength condition or polarization condition from apredetermined region of the specimen surface illuminated by theillumination lights; image-processing each of the plurality of imagesthat were detected, wherein the image-processing step provides a firstprocessing step and a second processing step: the first processing stepcalculates a plurality of feature quantities by processing each of theplurality of images and calculates defect candidates to the each of theplurality of images by processing the each of the plurality of featurequantities, and the second processing step sorts kinds of the defectcandidates calculated using the plurality of images in the firstprocessing step when at least one of the defect candidates is calculatedfrom the plurality of images in the first processing step.
 2. The methodthat detects defects of a specimen according to claim 1, wherein aplurality of images are detected by detecting a plurality of scatteredlights each having a different wavelength condition and polarizationcondition in the detecting step.
 3. The method that detects defects of aspecimen according to claim 1, wherein in the first processing step thedefect candidates are computed by a difference image of the imagesdetected in the detecting step.
 4. The method that detects defects of aspecimen according to claim 1, wherein the feature quantities computedin the first processing step are a maximum or an area of gray-scaledifference of the images.
 5. The method that detects defects of aspecimen according to claim 1, wherein kinds of defect candidatescomputed in the first processing step using all of the plurality of theimages are sorted in the second processing step when at least one ofdefect candidates is computed from the plurality of images in the firstprocessing step.
 6. The method that detects defects of a specimenaccording to claim 1, wherein the defect candidates computed in thefirst processing step are sorted into actual defects or pseudo defectsin the second processing step.
 7. The method that detects defects of aspecimen according to claim 6, wherein the actual defects are foreignmaterial, or etching residue, or a scratch, and the pseudo defects arebrightness unevenness of the oxide film, or roughness of the pattern, orgrain that have no criticality for a device.
 8. The method that detectsdefects of a specimen according to claim 1, wherein coordinates ofdefect candidates computed in the first processing step are outputted inthe second processing step.
 9. An apparatus that detects defects of aspecimen, comprising: an illuminating section that illuminates thespecimen surface with a plurality of illumination lights each having adifferent wavelength; a detecting section that detects a plurality ofimages by detecting a plurality of scattered lights each having adifferent wavelength condition or polarization condition from apredetermined region of the specimen surface illuminated by theillumination lights; an image-processing section that processes each ofthe plurality of images that were detected, wherein the image-processingsection provides a first processing section and a second processingsection: the first processing section calculates a plurality of featurequantities by processing each of the plurality of images and calculatesdefect candidates to the each of the plurality of images by processingthe each of the plurality of feature quantities, and the secondprocessing section sorts kinds of the defect candidates calculated usingthe plurality of images in the first processing step when at least oneof the defect candidates is calculated from the plurality of images inthe first processing section.
 10. The apparatus that detects defects ofa specimen according to claim 9, wherein a plurality of images aredetected by detecting a plurality of scattered lights each having adifferent wavelength condition and polarization condition in thedetecting section.
 11. The apparatus that detects defects of a specimenaccording to claim 9, wherein in the first processing section the defectcandidates are computed by a difference image of the images detected inthe detecting section.
 12. The apparatus that detects defects of aspecimen according to claim 9, wherein the feature quantities computedin the first processing section are a maximum or an area of gray-scaledifference of the images.
 13. The apparatus that detects defects of aspecimen according to claim 9, wherein kinds of defect candidatescomputed in the first processing section using all of the plurality ofthe images are sorted in the second processing section when at least oneof the defect candidates is computed from the plurality of images in thefirst processing section.
 14. The apparatus that detects defects of aspecimen according to claim 9, wherein the defect candidates computed inthe first processing section are sorted into actual defects or pseudodefects in the second processing section.
 15. The apparatus that detectsdefects of a specimen according to claim 14, wherein the actual defectsare foreign material, or etching residue, or a scratch, and the pseudodefects are brightness unevenness of the oxide film, or roughness of thepattern, or grain that have no criticality for a device.
 16. Theapparatus that detects defects of a specimen according to claim 9,wherein coordinates of defect candidates computed in the firstprocessing section are output in the second processing section.